NASCAR vehicles run hot and fast. It is the hot part that can be a problem. As in the oil temperature that can build in engines that produce up to 700-hp. The temperature can be as high as 245°F. Consequently, there has to be a method to keep things somewhat cool.
A source of radiators and oil coolers for several NASCAR race teams is C&R Racing of Indianapolis. In what is almost an irony, one of the engine oil coolers that C&R devised was actually doing too good a job. As C&R owner Chris Paulsen puts it, "That becomes a problem because the engine oil temperature can fall below the optimum for top engine performance. Since we can't lower the coolant temperature, we had to devise a variable bypass valve that would still keep a constant total flow of oil through the valve."
Paulsen designed the unit. It is a barrel-type rotary valve with 100% flow rate through an infinite adjustment range: all oil can go through the cooler or there can be complete bypass, depending on the conditions of the car.
There are four main pieces in the assembly: an aluminum body, barrel, cover plate and adjusting handle. The components were designed in AutoCAD. The CAD files were then brought into Mastercam, the CAM package that they've been using at C&R since 1994. Mastercam is developed by CNC Software (Tolland, CT).
Paulsen was concerned with more than designing and producing a system that worked. "We wanted a good-looking piece," he admits, "because racing television coverage often includes engine parts."
A more practical concern: weight savings. "Every ounce of material counts against a race car," Paulsen says, "so we wanted to radius all corners." So, after programming the outer contour to be cut with a ¾-in., two-flute end mill the program continues: it's right back along the same tool path, but with a 5/8-in. radius corner-rounding end mill.
Mastercam was used to circle-interpolate the barrel bore, which is 1.300 in. in diameter and 1.100-in. deep. With a Z-axis offset on the same center line, there's a 1.975-in. diameter pocket that's counter-bored to a depth of 0.187 in. It's used to register the barrel's cover plate.
Before any cutting was performed on the company's Protrak mill, Joe McCauley, C&R machinist, used Mastercam's solids-based toolpath verification feature to check the program. This feature runs each toolpath on a piece of "virtual stock," and provides the means to avoid gouging or tool damage. Speaking of this verification, Paulsen comments, "We do that with all parts because it makes it so easy to check everything as you go along."
All of the major components required for the cooler were programmed with the CAM software. In addition to drilling and milling there is also turning involved.
After the parts were machined, outer surfaces were black anodized. The handle for making adjustments, however, is colored flaming red. As Paulsen is sensitive to the way the product looks, the C&R logo was loaded into Mastercam, which wrote the toolpath for a cutter to incise the design into the cover plate.
Mastercam is used by C&R for the array of parts that it builds for several vehicle builders, such as aluminum transmission bell housings and suspension mounts for Riley & Scott and suspension parts, steering arms and various contoured aluminum mounts and brackets for Indy car builder Reynard Racing Cars. As Paulsen puts it, "Mastercam makes it really simple and fast to get a no-waste toolpath for a complex part."